1. Field of the Invention
The present invention relates to a method of manufacturing a light-emitting diode and more particularly to a method of manufacturing group III nitride semiconductor vertical type light-emitting diodes.
2. Description of the Related Art
Light-emitting diodes (LEDs) are widely used in many applications, such as exterior illumination lamps, interior lights, electric appliances requiring displays such as notebook computers, cellular phones, etc. Many direct-gap semiconductors have been used for fabricating LEDs. For example, gallium nitride (GaN) based LEDs are extensively used for emitting blue light because of its wide band gap (about 3.48 eV), higher light emission efficiency, high mobility, stable chemical properties and heat stability. In the current trend, a particular focus is also made on the development of LEDs, especially vertical light-emitting diodes (VLEDs), that have higher emission efficiency, higher yield and low fabrication cost.
Various approaches have been proposed for improving light emission of VLEDs. For example, one known approach consists of forming regular or irregular coarse patterns on the surface of various gallium nitride layers in the VLED to increase effective surface area of light emission. To this end, the gallium nitride layer structure of the VLED is usually formed on a surface of a sapphire substrate that is provided with regular or irregular uneven patterns. Then, the sapphire substrate is removed to obtain a multilayered structure with a coarse patterned surface. Two electrode structures are subsequently formed on two opposite sides of the multilayered structure, one on the coarse patterned surface, the other on another surface of the multilayered structure opposite the coarse patterned surface.
The regular or irregular uneven surface pattern can increase the effective emission area of the VLED, and reduce lattice mismatch for improving the crystalline quality of the epitaxy layer formed on the substrate. However, the uneven contact surface between the electrode and the multilayered epitaxy structure may result in non-uniform voltage distribution and higher resistance. One solution to this issue is to specifically leave an even and planarized area on the coarse surface of the sapphire substrate, such that the multilayered structure formed subsequently has a corresponding even contact surface for forming the electrode. This approach requires the application of a surface treatment on the sapphire substrate, which increases the cost of the substrate. In addition, while VLED structures require to form electrodes on opposite surfaces of the active multilayered structure, other LED structures (e.g., “horizontal” LED) may have all the electrodes formed on a same side of the multilayered structure and do not need such specifically-treated substrate.
Therefore, there is a need for a manufacturing method that can address the foregoing issues and fabricate a VLED in a more cost-effective manner.